Heat exchangers



July 7, 1959 Fgled Dec, 25, 1952 ,IJ jyjj w. HRYNlszAK 2,893,697

HEAT EXCHANGERS 2 Sheets-Sheet 1 /fyZ WHLDEMHR HRy/v/SZAK By July 7,1959 Filed Dec. 25, 1952 w. HRYNlszAK l 2,893,697

HEAT EXCHANGERS 2 Sheets-Sheet 2 Wnwemfm -HRf//v/SZAK l #ir /vfys l ,ili

HEAT EXCHAN GERS Application December 23, 1952, Serial No. 327,628

Claims priority, application Great Britain June v19, 1952 9 Claims. (Cl.257-.-1)

This invention ,relates to heat exchangers and more .specifically torecuperative heat exchangers wherein the vliow ,paths are of vsmallhydraulic diameter and particular care has to be taken that they do not`become clogged. v'The object of the present invention is to provideIcleaning means particularly suitable for cleaning such heat exchangers.

There are two known ways of preventing clogging ot a matrix, namely:

(1) By preventing the dust'from reaching the matrix;

(2') By cleaning the matrix to remove dust and other particles adheringthereto.

It is Anever quite possible to prevent all dust and the like particlesfrom reaching the matrix.

Where heat exchangers as referred to above are used in gas turbine plantclogging is liable to occur on both the air and the gas sides of eachelement.

If the air is properly tiltered at the compressor inlet the main .dangerof fouling will be on the gas side. This being the low pressure side ofthe preheater it is sensitive to pressure losses at all loads.

'This fact limits the use of method 1, because extracting dust from thegas increases the pressure loss.

As for method 2. when applied to a gas turbine plant, much depends on`the kind of fuel used and the form of dust obtained.

Method No. 2 may be suicient for certain, for example, high grade,fuels, which give only small particles of dust and few of them, but inother cases to apply this method to deal with the full amount of dirt ordust and other particles would mean that comparatively large equipmentwould be required or undue strain shown on the cleaning apparatus.

Referring to the accompanying drawings:

Figure 1 is a plan of a cell of a heat exchange element the cell beingin plan and of circular form;

Figure 2 is a section on the line A-A of Figure 1 looking in thedirection of the arrows;

Figure 3 shows in plan two cells arranged in a heat exchanger;

Figure 4 is a section on the line B--B of Figure 3 looking in thedirection of the arrows;

Figure 5 illustrates a diagrammatic arrangement of heat exchanger andcleaning device according to one form of the present invention.

Figures 6 and 7 are detailed diagrammatic views of part of Figure 5 to alarger scale for the purpose more fully of illustrating the corrugatedsheet arrangements and divisions or slits or spaces associatedtherewith, Figure. 6 showing corrugated sheets divided into two partsleaving a space with parallel sides and Figure 7 a space converging oneach side towards the centre of the corrugated strip.

In carrying the invention into effect in one form by way of example butirst describing a heat exchanger of the kind to which the inventionparticularly applies, a heat exchanger cell as shown in Figures 1 to 4comprises United States Patent O 2,893,697 Patented July 7, 1959 ICC aflat base sheet in the vform of a circular metal disc 1 .in which are`stamped two circular `locating holes 2.

Side walls 3 of the form shown in Figures l and 2 are aixed to disc 1 bybrazing or similar means locating holes 4 in these sidewalls coincidingwith the locating holes 2 of the metal disc 1.

In the space enclosed by the side wall 3 and metal disc 1 is fixed thematrix integer which consists of corrugated strip 5 as shown in Figure2. Cut in this strip are slits 6 which allow for expansion of theinteger at high temperature and they also enable the temperaturegradient per strip to be small. A cell is now complete and from it theheat exchange element is assembled or built up. A disc 7 of the nextcell identical with the disc 1 vis atlixed to the side walls and matrixby brazing or similar means. The flow path is contained between thediscs of adjacent cells, side walls and the corrugated strip.

In Figure 3 the gas inlet is at 7a, the gas outlet at 7b, the air inletat 7c and the air outlet at 7d.

In Figure 4 the gas passages are identied by the reference 7e and theair passages by 7f.

Further side walls 8 identical with side walls 3 are inverted and thenattached to disc 7 as shown, in a similar manner as before. In this waythe inlet and outlet channels for the gas flowing through this cell aredisplaced in an angular direction from the inlet and outlet of the iirstcell.

Another matrix of corrugated strip 9 identical with matrix 5 of cell 1is fixed by brazing in the space enclosed by side walls 8 and disc 7,this completing a second cell. Disc 10 is then fitted over the matrix tocommence a third cell.

The corrugated strip S divides the air stream into two parts 7f and thecorrugated strip 9 divides the gas stream into two parts 7e; the disc 7divides the air stream from the gas stream.

The discs, side Walls and corrugated strip are punched out to theappropriate size and assembled until a complete element is built up. Itis then usual to assemble a number of such elements in a casing to forma heat exchanger.

Two such elements indicated by the reference number 11 are assembled inopenings 12 of a casting 13 as shown in Figure 5, forming part of orused in conjunction with a gas turbine plant.

In that gure compressed air enters the heat exchanger through opening13a, passes through alternate cells of each heat exchange element, thatis to say through cells equivalent to those denoted by 7f in Fig. 4, andleaves in a preheated state through outlets 14 whence it is led to thecombustion chamber. Hot exhaust gas from the turbine is conveyed to theheat exchanger by duct 15. On leaving duct 15 it passes through a lter16 which removes any large particles contained in the gas and thenenters the heat exchange elements by openings 17 passes throughalternate cells equivalent to cells 7e in Fig. 4, where it gives up itsheat to the corrugated strip and adjacent metal discs and then leaves toexhaust by exit openings 18.

For the purpose of eiecting cleaning, the corrugated sheets are dividedinto two parts leaving a space 19 in between. This can be explained withreference to Figure 6. The spaces or passages 19 are formed by virtue ofthe fact that instead of being made as one piece as shown in the drawingof our British equivalent application referred to above, the corrugatedsheet insert is made in two separate pieces which, when inserted in thespace formed by the side wall, are of such a size that a gap or spaceexists between them and this gap is marked with the reference number 19.In the case illustrated in Figure 6 the gap is parallel sided and thetwo gaps of the corrugated sheet are marked 19a and 19b with expansionslits 19e and 19d, respectively.

Referring now to Figure 7 the corrugated sheets may be in two halves,are so shaped as toleave a converging slit between them. The corrugatedsheets are here marked 19e and 191, the openings which converge on eachside toward the centre of the corrugated strip being marked 19g. Figure7 also has arrows 19h applied illustrating the direction of gas owbetween the two halves 19e and 19j. The locating holes 4 of the sidewalls are made to accommodate tubes 20 (Figure 4) to provide passagesfor the cleaning air. Cut in the side walls are slits 21 which put thetubes into communication with the openings or space 19 in the corrugatedstrip. Slits 21a are also cut in the tubes 20 to put the slits 21 intocommunication with passages or spaces 19 or 19g, the slits 21 being cutin the side walls as previously stated. For a gas turbine it is suicientgenerally for these slits to be cut only in side walls on the hot gasside but depending on the circumstances all the side walls may haveslits cut in them to allow cleaning of each cell as opposed to the cellson the hot gas side only.

Cleaning air is forced through tubes 20 through slits 21 and throughopenings V19 where it spreads and flows in opposite directions througheach half of the corrugated strip. In this way dust or the likeaccumulating in the flow passages of the cells is removed together withthe dust which accumulates at the entrances and exists respectively.

Por this purpose compressed air may be tapped from a compressor or, asis preferred, supplied in short sharp blasts by means of a pump 22(Figure 5).

A valve 23 synchronized to operate in conjunction with the pump isarranged so that one of the two heat exchange elements 11, namely thatshown on the right hand side, working on the same hot gas side inlet 17can be cut olf from the flow of hot gases for the very brief periodduring which cleaning takes place. The valve is working in a lowpressure medium and is not subject to any pressures difference so that atight seal is not required.

When cleaning is about to take place the valve 23 is moved into the shutposition thus preventing the hot gas from entering the element 11,namely that shown on the right hand side of the drawing, through inletchannel 17 The other element, however, is still operating so thatcleaning does not interrupt the functioning of the heat exchanger. Byclosing the inlet in this way the gas collecting at entrance 17 is putinto communication with the suction ot pump 22 by `means of suction pipe24.

Movement of pump plunger 25 forces cleaning air or other iluid throughpipe 26 through tubes 20 of element 11 and hence into the channels ofthe cells of the element. Part of the air carries with it all the dustand other particles in the channels out to exhaust through duct 18.

The other part of the cleaning air leaves the inlet opening 17 nowclosed by valve 23 and is conducted away to the suction side of the pumpthrough opening 27 connected to suction pipe 24 on the return'stroke ofthe pump, carrying any dust collected with it.

The pump which is driven by a motor 28 but may be driven hydraulicallyor by other electrical means for example a solenoid, consists of thepiston or plunger 25 and a liner or cylinder 29.

On the upstroke of the plunger air is drawn in through filter Si) andinlet valve 31 whilst at the same time the dust-laden air collected onthe suction stroke is forced out to atmosphere through outlet valve 32.During this stroke valves 33 and 34 are closed.

On the downstroke valve 32 is closed and dust-laden air is drawn throughvalve 33 in connection with suction line 24. At the same time air isforced out through valve 34 into pipe 26 and hence to tubes 20 in theelement, the valve 31 being closed.

Thus air is forced through the tubes at regular intervals and hencethrough the slit in the side walls and through the channel between thetwo halves of the corrugated strip matrix and thence through the oWpaths of the matrix. In this way the dust accumulating in the owpassages of the gas side is removed with dust or other particlesadhering to the inlet and outlet of the cell.

Cleaning of the element on the left hand side is elected when the valve23 is switched over to the opposite position, shown dotted. In thisposition, the supply of cleaning uid to the element on the right handside would be cut ott, and the iluid supplied by ducts (not shown) butsimilar to 24 and 26 to the element on the left hand side of thedrawing. This switching of the cleaning uid from one element to theother can be effected by any suitable means such as a rotary valve whichwould allow cleaning iluid to be supplied and withdrawn by the pump fromonly one element at a time.

The pump intake air can be cleaned to a high degree since only smallamounts of cleaning air are needed at one time. The pump delivery valvemaybe spring loaded to enable the pressure to be varied. If a by-pass isprovided the amount of cleaning air as well as the delivery pressure canbe selected to suit the particular conditions and the same applies tothe frequency of the air deliveries.

Cleaning of the element may be improved by providing certain adjustmentsto suit the working Vconditions such as:

(a) Proper location of the slits 19 to obtain maximum possible amount ofcleaning for example by placing the slits closer to the inlet 17 of theelements and the matrix, the cleaning air due to decreased pathresistance will travel to a greater extent in a direction opposite tothat of the gas ow provided that the influence-of the dynamic pressurebe allowed for.

(b) Altering the resistance to ow of the corrugated strip by usingdiierent sizes of corrugations for the strip at the inlet and outlet ofthe cell. For example, we could make corrugations`19d larger thancorrugations 19e to help induce the cleaning fluid to llow more easilytoward inlet 17. Y

(c) Avoiding sharp edges and corners in the inlet and outlet ducts 13aand 17, 14 and 18 and the inlet and outlet edges of the corrugated stripso as to give the dust as much chance as possible to escape with thecleaning air.

In the case of round cells, the corners o'f the corrugated strips may becut off so as to allow the dust to escape freely where these edges touchthe side walls. The round cells have a rather more pronounced deflectionbecause of the difference in the extent of the inlet and outlet openingscompared withthe matrix opening.

When the matrix is cleaned by blowing air through the channels of itshot gas side 'as described above, one part of the dust-laden cleaningair passes through the exhaust system to the open. The other parttravels in the opposite direction against the flow of the hot gases, sothat the dust removed by this portion of the air tends to remain in ornear the hot gas side inlet of the cell and continuously adds to thedust content of the hot gas unless the dust is removed by suitablemeans. Such removal is of importance, as the bulk of the dust willcollect at the hot gas side inlet of the element in general, and at theinlet of its matrix in particular.

In heat exchangers of the type described the elements can be arranged inany suitable form preferably so that their hot gas sides can be fed froma common inlet-duct. A filter is preferably arranged in the inlet ductof the hot gas to prevent any -large particles entering the matrices ofthe cells comprising each heat exchanger element.

The cleaning mechanism is automatic and continuous and has the advantagethat in a heat exchanger consisting of a number of elements a very smallpercentage of the total number of elements are being cleaned for a veryshort period and the eiiciency of the heat exchanger is not adverselyimpaired.

The system can apply to heat exchangers of both the counter ow and crossflow'types and canbe used in plants other than the gas turbine. Thecleaning uid need not be air but may depend upon the nature of theparticles adhering to the ma `trix for any given reason.

The pump may be replaced by using air from the compressor in a gasturbine plant.

What is claimed is:

l. A method of maintaining clean heat exchanger surfaces in arecuperative heat exchanger, havi-ng relatively stationary heat exchangepassages and inlet and outlet passages, which comprises filtering a gasto remove at least part of any dust therein, and passing the filteredgas through a heat exchanger matrix, and intermittently introducing airinto the said matrix intermediate its inlet and outlet ends and blowingthe air through the matrix toward both the inlet and exhaust passages toremove any unfiltered dust and other particles adhering thereto.

2. A method according to claim 1 in which the prevention of the dustfrom reaching the matrix is elected by filtering the gas at the inlet ofthe gas side of the heat exchanger.

3. A method according to claim 1 in which the blowing of air through thematrix is effected periodically and automatically whilst the heatexchanger is in operation and in timed relation to a gas turbine,through which gas from the heat exchanger is passed and from whichexhaust gas is passed through the heat exchanger.

4. A method according to claim 3 in which only the gas side of the heatexchanger matrix is periodically and automatically cleaned.

5. A method according to claim 1 in which the cleaning air is introducedinto a space dividing the ilow paths of the matrix into two parts.

6. A method according to claim 5 in which at least part of thedust-laden cleaning air is drawn off by suction.

7. A method according to claim 6 in which at least one opening of thegas side of the matrix is closed whilst the matrix is being cleaned.

8. A method according to claim l in which the cleaning air is mixed withan additional cleaning iluid.

9. A recuperative heat exchanger having relatively stationary heatexchange passages and inlet and outlet passages, said heat exchangercomprising one or more heat exchange elements, each element consistingof a number of cells arranged in the form of a column or stack, eachcell consisting `of a llat base sheet and side walls which deiine a lloWchannel, said ow channel being further subdivided into a number of ilowpassages by two corrugated strips spaced apart from each other in thedirec# tion of flow therethrough, cells containing hot iluidalterntating with cells containing cold iluid, means for ltering theheat exchanging uids prior to their entry into the flow passages andmeans for introducing a cleaning ilud into the space separating saidcorrugated strips causing said fluid to ow in opposite directionsthrough each strip towards the inlet and outlet ends of said passages toremove any unfiltered dust or other particles adhering thereto.

References Cited in the le of this patent UNITED STATES PATENTS1,558,445 Ljungstrom Oct. 20, 1925 1,680,145 Forssblad Aug. 7, 19281,858,508 Kignell May 17, 1932 1,903,650 Snow et al Apr. 11, 19331,970,127 Colby et al Aug. 14, 1934 2,288,061 Arnold June 30, 19422,673,446 De Salardi Mar. 30, 1954 l. FOREIGN PATENTS 462,857 GreatBritain Mar. 17, 1937

